Climate change is evident in the data for Marlborough over the past thirty years. It is particularly seen in the data for heavy rainfall and temperature.
Comparing the mean temperatures for both maxima and minima during the spring season, there is an almost continuous upward trend. The mean figure for spring in the 1980s was 7.7°C but by 2013 this had risen to 8.8°C. The very cold springs of 1996 and 2013 produced a blip in the trend but a difference of approximately 1.1°C is quite significant. The upward trend becomes stronger moving from March through to May.
Linked with the temperature results is the occurrence of air frosts. Breaking down the years since 1990 into five-year groups I find that the incidence of the last air frost in spring, on average, has moved successively backwards from 11th May to 5th May, 16th April and 21st April. The four-year group from 2010 to 2013 has an average of 20th April but as we are experiencing a mild start to the year this average is likely to move further backwards.
There is a similar trend to the first occurrence of an air frost in the autumn. Using the same five-year groupings the average has moved successively from 22nd September to 9th October, 18th October and 26th October. The result of the four-year group for 2010 to 2013 is now 4th November.
Rainfall has been very much in the news during the last few months, including the flooding in Marlborough. Warmer air holds more moisture so it is logical to expect rainstorms to show evidence of this fact. Over the last thirty years there is an increasing trend for the incidence of heavy rain in Marlborough. Analysing the data further and breaking it down into groups of heavy rainfall I find that the daily totals of up to 10mm have increased by 7, 20mm by 2 and 25mm by 1. Not surprisingly, the summer months of July and August show the greatest increase.
In January and February 2014 my 30-year records for monthly rainfall were broken with totals of 219.1mm and 151.6mm respectively. Daily records were also broken for both these months along with December 2013.
